Composition comprising lead azide or lead styphnate and molybdenum disulphide



United States Patent Ofifice 3361,62 Patented Jan. 2, 1968 3,361,602 COMPOSITION COMPRISING LEAD AZlDE R LEAD STYPHNATE AND MOLYBDENUM DISULPHIDE James Patterson McNicoll Leslie, Stevenston, Scotland,

assignor to Imperial Chemical Industries Limited, London, England, a corporation of Great Britain No Drawing. Filed July 28, 1966, Ser. No. 568,399 Claims priority, application Great Britain, Aug. 9, 1965, 34,008/ 65 11 Claims. (Cl. 149-24) ABSTRACT OF THE DISCLQSURE The inclusion of up to about 4% powdered molybdenum disulphide in lead-aZide-containing detonator compositions reduces the tendency of the compositions to adhere to the press punch which is conventionally employed to press the compositions into casings. The molybdenum disulphide may be incorporated by first dispersing it in a colloid solution and subsequently precipitating lead azide from the solution by the conventional technique of adding a water-soluble azide and a water-soluble lead salt. Alternatively dry molybdenum disulphide may be mixed with dry lead azide.

Disclosure This invention relates to lead azide compositions suitable for use as primary initiating explosive compositions (hereinafter referred to as the primary charge) in detonators and to processes for the preparation thereof.

In the manufacture of detonators containing lead azide in the primary charge the lead azide is pressed, by a punch, at a high pressure into a tubular casing on top of a base charge of secondary explosive. The lead azide used hitherto has tended to adhere to the pressing punches giving rise to risk of accidental explosion on Withdrawing the punch, due to the sensitivity of the lead azide to friction. This risk is increased if the lead azide primary composition contains, as it often does, lead styphnate (lead trinitroresorcinate) to increase the cohesion and the sensitivity to initiation by burning safety fuse, since the lead styphnate has an even stronger tendency to adhere to press punches. Hitherto lead azide compositions have usually contained a small proportion of fine aluminum to act as a lubricant to prevent adhesion to the punches but the aluminum increases the sensitivity of compositions containing lead styphnate to ignition by electrostatic discharge and is generally inconvenient in detonator manufacture because the dry mixing process by which it is incorporated is conducive to the accumulation of electrostatic charge and to the spread of the dry aluminum as airborne dust.

It is an object of the present invention to provide a lead azide composition free from aluminum and having reduced tendency to adhere to press punches.

We have discovered that molybdenum disulphide is effective in treating lead azide to reduce its adhesion to press punches and that this treatment is also effective for lead azide primary charges containing lead styphnate.

Thus in accordance with this invention a lead azide composition suitable for use in a detonator primary composition comprises lead azide and molybdenum disulphide. Optionally the composition may also comprise lead styphnate.

The molybdenum disulphide is preferably in the form of a fine powder having an average particle diameter size of less than 20 microns.

A marked reduction in the tendency of the lead azide composition to adhere to the press punches can be accomplished by the use of small proportions of molybdenum disulphide. For practical purposes it is not usually necessary to use more than 4% by weight of the composition and a high degree of freedom from adhesion can be achieved by using 0.1% by Weight.

The lead azide composition of the invention may be prepared by mixing the molybdenum disulphide with the lead azide in the dry state but in a preferred method it is dispersed in a liquid medium, conveniently water, before mixing with the lead azide. Since the lead azide is invariably formed by effecting the formation of a solid precipitate in an aqueous solution of a colloid, such as, for example, gelatine or dextrin, by reacting a waters'oluble azide and a water-soluble lead salt, it is advantageous to disperse the molybdenum disulphide in the said colloid solution. The colloid solution usually contains in solution caustic soda, Rochelle salt and a colloidal material such as, for example, gelatine or dextrin, or a mixture thereof, and a dispersion of molybdenum disulphide can be readily prepared in such solution. It is preferred, however, to avoid using dextrin as the colloid since the azide crystals formed in presence of dextrin and molybdenum disulphide are rather sensitive to grit and electrostatic discharge. An azide having slightly better cohesion is obtained if the caustic soda is omitted. A Wetting agent dissolved in the colloid solution accelerates the dispersion of the molybdenum disulphide. It is only necessary to use a slight excess of molybdenum disulphide since nearly all becomes mixed with the lead azide. In this form of the process a high proportion of the molydenum disulphide is bound within the lead azide crystal structure and higher concentration of molybdenum disulphide tends to give a product of reduced crystal size.

Compositions containing lead styphnate may be prepared by adding the molybdenum disulphide to a preformed mixture of lead azide and lead styphnate but it is more convenient to treat the lead azide separately with molybdenum disulphide and subsequently to incorporate the lead styphnate which may, if desired, also be treated with molybdenum disulphide prior to its incorporation. The treatment may advantageously be elfected by forming a lead styphnate precipitate by reaction of a water-soluble lead salt and a water-soluble styphnate in an aqueous solution of a colloid in presence of a dispersion of molybdenum disulphide.

In addition to having reduced tendency to adhere to the press punches, the lead azide compositions of the invention, including those containing lead styphnate, are satisfactory in all other important respects. For example, the sensitivity to ignition by electrostatic discharge and by burning safety fuse is not materially affected and its ability to initiate secondary explosive is somewhat enhanced.

The invention is further illustrated by the following examples in which all parts and percentages are by Weight.

Examples ]-16 In these examples, details of which are given in Table l, 50 cc. of each of two aqueous solutions, one containing 38.3% of lead nitrate and the other containing 15% of sodium azide and 0.057% of Rochelle salt, were run simultaneously at a uniform rate over a period of 32 minutes into 337 cc. of a base solution containing 0.5% of a colloid and having dispersed therein a quantity of molybdenum disulphide as indicated in Table 1. The molybdenum disulphide had an average particle size of less than 20 microns. The resulting precipitate of lead azide was separated, washed with Water, dried in air at 5060 C. and tested. In Examples 1-15 the colloid was nonfoaming gelatine containing 0.2% of n-octyl alcohol as antifoaming agent, and in Example 16 it was dextrin. In Examples 2 and 4 the solution containing the sodium azide also contained 0.12% of caustic soda. In Examples 6-16 inclusive the base solution contained one drop of a wetting agent available commercially as Lissapol NX (Registered Trademark) to facilitate dispersion of the molybdenum disulphide.

Samples of the material were tested for cohesion, grit sensitivity, sensitivity to electrostatic discharge and bulk density as described in the specification of United Kingdom Patent No. 961,787 except that in the test for sensitivity to electrostatic discharge, material which had been pressed at 6000 p.s.i. and subsequently broken down was used. The results obtained are recorded in Table 1. In addition the samples were tested for sensitivity to friction and impact, their ability to be ignited by safety fuse, their ability to initiate a detonator base charge of pentaerythritol tetranitrate (PETN) and their ability to flow through an orifice. The azide of Examples 1-15 was in all these respects superior to similar lead azide compositions not containing molybdenum disulphide. The lead azide of Example 16, wherein dextrin was used as the colloid, was in the form of irregular sharp-pointed crystals which had for their tendency to adhere to press punches. The results show that the mixtures were as suitable for use in detonator initiating explosive charges as pure lead azide except that with the higher molybdenum disulphide concentrations the amount required to initiate PETN was higher.

When 71 parts of the compositions of these examples were mixed with 29 parts of lead styphnate the resulting mixtures were as good initiating explosive compositions as the ASA composition commonly used and did not exhibit any greater tendency to adhere to press an undesirably high grit sensitivity and was also rather punches.

TABLE 2 Sensrtwrty Mnumum Molybdenum Bulk Cohesion Grit to electroquantity to Ex. disulphide density tmins.) sensitivity static disinitiate a (percent) (g./cc.) (g. cm.) charge PETN bnse (kilovolts) charge (g) 1 1. 47 60 50 15-18 0. 02-0. 03 2 1. 47 60 50 18 0. 03-0. 04 3 1. 47 60 50 18 0. 03-0. 04 b l. 47 00 50 18 0. 04-0. 05 N11 1. -7 60 42-50 10-15 0.02-0.03

and did not exhibit any greater tendency to adhere to 50 press punches.

What I claim is: 1. A composition suitable for use in a detonator primary charge comprising lead azide and molybdenum disulphide.

2. A composition as claimed in claim 1 comprising additionally lead styphnate.

3. A composition as claimed in claim 1 wherein the molybdenum disulphide is in the form of a fine powder 5 having an average particle diameter size of less than 20 microns.

4. A composition as claimed in claim 1 containing 0.1 to 4% by weight of molybdenum disulphide.

5. A lead styphnate composition suitable for use in detonator primary compositions comprising lead styphnate and molybdenum disulphide.

TABLE 1 Molybdenum Lead azide Molybdenum disulphide content of lead Bulk Grit Sensitivity to Ex. disulphide 111 content of lead azide density, Cohesion sensitivity, electrostatic Remarks base solution, azide precipitate, g./cc. (minutes) g. cm. discharge percent precipitate, percent (kilovolts) percent 0.1 2.04 92. 5 1. 40 60 7-10 0.1 2. 04 91. 6 1 40 50 10-15 NaOH in sodium azide o. 05 1. 10 93. 7 1. 37 60 33-42 7-10 solution 0. 05 1. 10 92. 7 1. 37 60 33-42 5- 7 D0. 0. 075 1. 93. 4 1. 40 60 33-42 10-15 0. 0045 0. 1 94. 8 1. 51 60 42-50 15-18 0. 022 0. 45 94. 5 1. 40 60 42-50 7-10 0. 04 0. 92 94. 2 1. 47' 60 42-50 10-15 0. 006 1. 4 93. 6 1. 47 00 50 10-15 0. 09 1. 93. 5 1. 30 60 42-50 5- 7 0. 102 2. 4 92. 9 1. 47 60 33-42 5- 7 0. 13. 2. 85 92. 2 l. 47 60 42-50 5- 7 0. 18 3. 6 91. 5 1. 47 60 33-42 10-15 0. 22 4. 5 91. 7 1. 47 60 50 15-18 0. 23 4 91. 2 1. 47 60 33-42 7-10 0. 1.12 a. 3 92 1. 43 60 8-17 3- 4 NaOH in sodium azide solution and dextrin in base solution.

1 NaOII present.

8. A process as claimed in claim 7 wherein the gelatine 10 is a non-foaming gelatine.

9. A process as claimed in claim 8 wherein the gelatine solution comprises n-octyl alcohol as an anti-foaming agent.

10. A process as claimed in claim 6 wherein the aqueous solution comprises a wetting agent.

11. In the process of manufacturing a lead styphnate composition for use in a detonator primary charge by precipitating lead styphnate from an aqueous colloid solu- 6 tion by adding thereto a water-soluble styphnate and a water-soluble lead salt the improvement which comprises dispersing molybdenum disulphide in said solution before precipitating lead styphnate.

References Cited UNITED STATES PATENTS 8/1966 Leslie l49-35 11/1966 Rothstein et al. l49-23 OTHER REFERENCES Fedorofl; Encyclopedia of Explosives and Related Items, vol. I, Picatinny Arsenal, Dover, N.J., 1960, pp. 576-580.

15 L. DEWAYNE RUTLEDGE, Primary Examiner.

CARL D. QUARFORTH, Examiner. L. A. SEBASTIAN, Assistant Examiner. 

